The current focus in high-energy physics is the study of the properties of the Quark Gluon Plasma (QGP) in Heavy-Ion Collisions (HICs). The interpretation of experimental data with respect to the properties of the QGP requires precise understanding of all hadronic interactions, which have to be implemented in transport theoretical models and their influence has to be tested in comparison with experimental data. The significance of the baryon-antibaryon annihilation and reproduction in the strangeness sector for particle spectra from HICs has not yet been clarified. Particularly the reproduction by more than two mesons is not taken into account in most of the transport theoretical models, although the production threshold is reduced by the reaction of several particles and thus should have a significant contribution. This work is devoted to this question and examines the baryon-antibaryon annihilation and reproduction in relativistic HICs.As a first step the baryon-antibaryon annihilation and reproduction is extended to the strangeness sector in the Parton-Hadron-String Dynamics (PHSD) transport approach. In addition to the baryon-antibaryon $leftrightarrow$ 3 mesons reactions ($Bbar Bleftrightarrow 3M$), matrix elements for channels with single and multiple strangeness have to be specified. In this thesis, a suppression parameter $lambda$ is introduced, which is motivated by the larger mass of the strange quarks relative to the light ($u,d$) quarks. The final results are presented and discussed as an explicit function of $lambda$. The reliability of the numerical implementation is confirmed by tests of the detailed-balance relations in box simulations with periodic boundary conditions. Subsequently, the influence of the $Bbar Bleftrightarrow 3M$ reactions on particle spectra in PHSD simulations of HICs in the energy range from FAIR/NICA to LHC will be investigated, i.e. $sqrt{s_{NN}}=7$,GeV to 2.76,TeV. The investigations show that below $sqrt{s_{NN}}=130$,GeV the $Bbar Bleftrightarrow 3M$ channels have almost no influence on meson and baryon spectra; only the antibaryons are affected. The $Bbar Bleftrightarrow 3M$ channels --- including the strangeness sector --- influence the antibaryon rapidity spectra in the lower SPS energy range $sqrt{s_{NN}}<7$,GeV more strongly than in the upper SPS energy range of $sqrt{s_{NN}}approx 17$,GeV and result in a better agreement of the PHSD results with experimental data. At ultra-relativistic energies of RHIC and LHC ($sqrt{s_{NN}}>20$,GeV) the baryon sector is affected by the $Bbar Bleftrightarrow 3M$ channels as well and the description of experimental data is generally improved. We, additionally, examine the difference between calculations with the full $Bbar Bleftrightarrow 3M$ reactions to calculations that only consider annihilation, corresponding to the procedure of other current transport approaches. In the antibaryon sector we find deviations of up to a factor of 2.5, with the largest deviations at the lower SPS or FAIR/NICA energies.
